The present invention relates to a teat cup for milking systems, with an outer sheath that surrounds an inner sheath, leaving between them a pulsation space that is alternately subjected to vacuum and to atmospheric pressure, whereby the interior of the inner sheath communicates with a vacuumized line and a valve automatically prevents flow from the line into the interior of the inner sheath.
Teat cups of this type are known. The valve is a check valve and is positioned either on the cup or in the line, which leads from the interior of the inner sheath to a milk-removal line. The valve is intended to prevent milk that has already been extracted from the udder from flowing back into the inner sheath, where it might lead to infection of the teat.
Although the valve in the known cup does prevent backflow, it also involves the drawback of leading to too powerful a vacuum below the teat during the suction phase of the milking process. This vacuum is generated by the inner sheath itself when the valve is closed, and is more powerful than the operating pressure prevailing inside the inner sheath. During the non-suction phase, the inner sheath is compressed by the atmospheric pressure in the pulsation space, for which the tensional force on the part of the inner sheath must be overcome. During the subsequent suction phase, when the inner sheath is expanded, the valve closes subject to the resulting backflow, which happens before the cross-section of the sheath is completely open. Since the interior of the inner sheath has been subjected to operating vacuum before the valve closes, the sheath will, as it continues to expand once the valve has closed, increase the vacuum in its interior even more. The extent that the vacuum increases to can vary widely, depending on the age and flexibility of the inner sheath, and can be impermissibly high. Furthermore, the vacuum below the teat during the non-suction phase may not, commencing from a very high level during the suction phase, decrease adequately. This can eventually lead to evagination of the udder stroke channel and other serious udder problems.